At present, microcomputer systems own the capabilities of high-speed computing and storing data. In modern electrical systems, controllers composed of microcomputers have already replaced the past purely mechanical or electrical-mechanical control mechanisms. The signals inside a microcomputer are digital, which is represented by logic “0” or “1”. Logic “0” represents a low voltage level, which is generally 0 volt in the microcomputer system; logic “1” represents a high voltage level, which is generally 5 volts in the microcomputer system. However, in the physical world, physical quantities usually exhibit continuous analog signals. Thereby, for transmitting the variation of external physical quantities to a microcomputer for operations, or for driving devices by outputting commands from a microcomputer, it is required to convert the signals.
General continuous signals such as measured voltage or current are analog signals. The converter converting analog signals to digital signals is called an analog-to-digital converter (ADC), which can be classified according to the conversion methods into digital-ramp ADCs, successive approximation ADCs, flash ADCs, and tracking ADCs. These ADCs can acquire analog signals, process the analog signals, and convert them to digital signal.
On the other hand, a digital-to-analog converter (DAC) is a common circuit element in various electronic apparatuses. DACs produce corresponding analog outputs according digital inputs for backend circuits. DACs rely on unit elements (resistors, capacitors, or current sources) for converting. However, mismatches must exist among components, particularly for integrated circuits. For current-controlled DACs in high-speed and high-resolution applications, mismatches among current sources pose a serious problem, which will result in distortion noises. For suppressing the distortion noises, the technique of dynamic element matching (DEM) is applied. Nevertheless, for applications requiring a larger number of conversion bits or faster conversion speed, DEM cannot suppress the distortion noises effectively. Thereby, how to reduce the distortion noises in DACs has become the most important issue in the present day.
Accordingly, the present invention provides a DAC, which can reduce the distortion noises, and hence the problems occurred in the prior art as described above can be solved.